Hollywood's Super Hero Easter Eggs That Paid Off -- And Some That Didn't

"Arrow" fans got a big surprise during last week's "Suicide Squad" episode of the CW's drama series. Fan favorite troublemaker Harley Quinn made a cameo appearance, or rather her voice did. Actress Tara Strong, who voiced Harley on "Batman: The Animated Series," the "Batman: Arkham" and "Injustice: Gods Among Us" video games and pretty much anywhere else the Joker's sometimes sweetheart has been heard, delivered the dialogue in question, confirming that there is indeed a Harleen Quinzel locked up in the "Arrow"-verse. Still, that doesn't mean Harley is a lock to have a future in Starling City.

"I want to manage expectations with respect to Harley Quinn," "Arrow" executive producer Marc Guggenheim warned fans. "She was always intended to be an Easter egg." Of course, as comic fans well know, Harley's one line of dialogue is just the latest in a long line of Easter eggs found in super hero adaptations. With that in mind, CBR takes a look at some of the biggest ones that paid off -- and a few that should have just stayed hidden.

As one of the most popular X-Men of all time, fans were justifiably bummed when Rogue took Kitty's place as the entry point character in the first X-Men film. Those fans were then treated to a scene where a smartly dressed schoolgirl runs through a wall, much to Wolverine's surprise. We got another display of Kitty's powers in "X2: X-Men United" during Stryker's raid on the X-Mansion, but she didn't become a major player until "X-Men: The Last Stand." While that film was met with a less than positive fan reaction, audiences were generally pleased with Ellen Page's depiction of the character. She's even playing a pivotal role -- albeit less pivotal than the role she played in the comics -- in this summer's "X-Men: Days of Future Past." This Easter egg paid off.

Eddie Brock in "Spider-Man" (2002)

Super Spider-Man fans knew that when Robbie Robertson uttered the name "Eddie" in Sam Raimi's first Spider-film, he meant Daily Bugle photographer Eddie Brock. While that reference might have flown under the radar of casual Spidey fans, they definitely would have caught it had Raimi name-dropped Eddie's alter-ego -- Venom. Sadly, when the trilogy finally got around to giving Eddie Brock some screentime in "Spider-Man 3," fans immediately regretted it. Topher Grace's menacing performance got lost in all of the dance numbers, amnesia plotlines, and other super villains that appeared in the film. This Easter egg did not pay off.

Nick Fury in "Iron Man" (2008)

There's maybe no greater Easter egg in all of comic-dom than Samuel L. Jackson's surprise appearance after "Iron Man's" credits. With a short appearance, Marvel revealed the existence of a wider movie-verse and kicked off the events that would lead to "Marvel Studios: The Avengers" four years later. And while movies had employed the post-credits scene schtick for years, Fury's debut made sticking around until the very end a necessity for every comic book movie. This Easter egg paid off, in a huge way.

Robin John Blake in "The Dark Knight Rises" (2012)

Unlike a lot of people on this list, Joseph Gordon-Levitt's cop character from the final installment in Christopher Nolan's Bat-trilogy played a huge part throughout the entire film. The Easter egg-ness of his character wasn't revealed until his next to last scene in the film, when he reveals his full name in order to claim his Bat-inheritance -- Robin John Blake. The "Robin" part was obviously a shout-out to Batman's iconic sidekick, but fans hoping to see John Blake assume the mantle like Dick Grayson had in the comics, were left sorely disappointed. Instead of continuing this Robin's journey, Warner Bros. hit the reset button, resulting in Ben Affleck's upcoming debut as the Dark Knight. This Easter egg did not pay off.

Captain America in "Iron Man" (2008)

More accurately, Captain America's shield appeared in "Iron Man" during the scene where Pepper Potts first discovers Tony's alter ego. The shield, an unfinished version of Cap's iconic accessory, appeared again in 2010's "Iron Man 2," where it was unceremoniously used to prop up one of Tony's inventions. Both of these appearances, along with a deleted scene from "Incredible Hulk" wherein Cap's frozen body and shield can be seen encased in Arctic ice, all paid off when Steve Rogers burst onto the big screen in 2011's "Captain America: The First Avenger." So yeah, these Easter eggs paid off.

Emma Frost in "X-Men Origins: Wolverine" (2009)

There are more than a few continuity errors that arise when one tries to synch Fox's original "X-Men" trilogy up with Matthew Vaughn's "X-Men: First Class," and almost all of them stem from Wolverine's first solo outing. One of the biggest inconsistencies is Emma Frost. In "Origins," which is set in the early '80s, Frost is Silverfox's teenage sister. In "First Class," famously set in 1962, she's an adult woman. Not only did this Easter egg not pay off -- it causes more headaches than it's worth, especially considering how iffy fans were on "Origins," and the fact that it preceded one of "First Class'" less memorable performances.

The Ten Rings in "Iron Man" (2008)

Judging by this list, "Iron Man" might be the biggest superheroic cinematic Easter egg basket around. When a terrorist organization was dubbed the Ten Rings, fans immediately connected the dots to form an image of Iron Man's longtime arch-rival, the Mandarin. Immediately, we could see it -- Robert Downey Jr.'s Tony Stark going up against the Mandarin's powerful ten rings in a future "Iron Man" film. That's what we thought we were getting in "Iron Man 3" when Sir Ben Kingsley landed the Mandarin gig. But things didn't really play out like that, did they? The Mandarin was revealed to really be Trevor Slattery, a bumbling English actor that got paid in booze. This reveal angered some fans, while Sir Ben's doofy antics delighted plenty of moviegoers. This Easter egg paid off for some and just enraged others.